The heart of the fish: Who is not afraid of a heart attack
The heart of a small aquarium fish Danio ( Danio rerio ) has amazing abilities. It continues to beat even - literally - even pierced through. And even if 20% of the ventricular tissue is removed, the heart blocks blood loss in seconds, and the cells begin to gradually recover. About a month later, the fish swim again, as if nothing had happened.
Interestingly, all this repair is done without stem cells. It would seem that it is from them that, through development and differentiation, a new tissue of the heart muscle should be formed. But in fact, everything is done by the "mature" heart cells themselves.
This question generally has long been occupied by scientists: what is the role of stem cells in the process of regeneration of organs and tissues in animals with a pronounced ability to it - in the same zebrafish, salamanders, and so on? Until now, it was difficult to say whether stem cells develop in the tissue being restored, or whether "adult" cells of this tissue are already involved in this process. Recent studies have shed light on this problem.
To understand the matter, Spanish and American scientists led by Juan Carlos Belmonte created a genetically modified line of zebrafish, in which cardiomyocytes, muscle cells, were fluorescence-capable. Then they surgically removed 20% of the ventricular tissue (recall that the fish has a two-chamber heart, consists of 1 atrium and 1 ventricle) - and they observed the regeneration process.
As these experiments showed, the newly formed tissue of the heart muscle also fluoresced. This means that it comes precisely from cardiomyocytes, which transmitted this ability to offspring, and not from stem cells. A more detailed study made it possible to establish that after an injury, the cardiomyocytes surrounding the site of damage undergo an amazing transformation - as if a step back in development, losing their shape and connection with each other. Apparently, this allows them to again begin to divide and form new cells.
A group of American researchers led by Kenneth Poss came to a similar result. In fact, the idea in their experiments was the same, although the details were different. They also created a modified line of zebrafish, whose cells fluoresce if the gata4 gene is activated. Normally, this gene is active only in the heart and only in embryos, while they are developing this organ. It turned out to be active in fish after a heart injury.
The next step, of course, should be the identification of cellular signals that trigger the regeneration process. And there, the prospects are simply amazing, from the complete cure of people who have had myocardial infarction to ... yes, even to the "regrowth" of new healthy organs in return for having served their own.
By the way, these fish are far from being the first to appear as objects of very interesting scientific research. Take at least neurophysiology: it was zebrafish that made it possible to better understand the structure and operation of our brain. Read: “Brain Control, ” “Battle of the Hemispheres.”
According to ScienceNOW